Glial Cells and Polyamine Signaling in the Central Nervous System

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Project Summary/Abstract (from Parent grant): Emerging recent publications show that polyamines (PAs) are key players in the exceedingly common disorders of aging and HIV associated neurocognitive disorders (HAND), Alzheimer's, Huntington's and Parkinson diseases as well as in Snyder-Robinson and SeSAME/EAST syndromes. PAs are released in whole brain from unknown sources during neuronal activity and trauma. PAs demonstrate neuroprotection against neurotoxicity, ischemia, brain injury and also increase longevity. Since PA content declines with aging or during pathology, the neuroprotection afforded by PAs can decline as well. This substantially increases the risk of morbidity and mortality. Despite its public health importance, relatively little is known about PA fluxes in brain and insufficient attention is paid to glial cells in CNS. Intriguingly, we found that in healthy adult brain and retina, glial cells but not neurons accumulate preferentially PAs such as spermidine (SD) and spermine (SP). We further recently found that PAs are the major openers of astrocytic connexin-43 (Cx43) gap junctions (GJs). Therefore, since Cx43 GJs are the major communicating channels between astrocytes, PAs keep glial syncytium integrity that may help to hold healthy brain status, however in many (patho)physiological conditions the situations are not well studied. The storage of internal PAs and their effects regulated by glia on brain function are some of the remaining mysteries and our findings raise key questions: (i) What are the mechanisms that underlie such uneven distribution and accumulation of PAs between astrocytes and neurons? (ii) What are the mechanisms of PA release in CNS from glia? (iii) What are the consequences of PA fluxes within the brain on neuronal function? and (iv) Ultimately, what are the roles of PAs in brain disorders and diseases? The glial PA pathways hitherto have been neglected, although it is evident that these molecules are key elements for normal brain status and their metabolic disorders, apparently, cause the development of many pathological syndromes and diseases. We have developed techniques for measuring PA fluxes in brain slices and retina and will use transgenic animal models of HAND (and in the future of other diseases) to study (patho)physiology of PA translocation. In this project, we will test the original hypothesis that PAs are novel “gliotransmitters” that (i) are transported into glia, (ii) open astrocytic intercellular gap junctions, (iii) propagate in the astrocyte-to-astrocyte syncytium (AIM-1) and (iv) are released from glia upon local stimulation (v) to regulate the neuronal-glial network (AIM-2). We will address these two aims to determine mechanisms of PA uptake/accumulation/release/signaling in CNS. The studies will lead to new scientific knowledge and research opportunities for graduate students to further understand neurodegenerative processes, helping advance diagnosis, treatment and prevention.